Physics 133
Spring Quarter 2004
28 April 2004
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The quiz is due before class today, 28 April 2004.
If the principal quantum number n allows n - 1 for the angular momentum quantum number, how come there are several similar periods in the periodic table (for example, for n = 2 and n = 3 the periodic table appears identical)? Explain.
Gordon’s solution will appear here
The periods result from the process of filling in the lowest-energy electron states. The number of electrons is fixed at the number of protons in the nucleus, Z. The Pauli Exclusion Principle mandates that there be only one electron in each state within the atom. (Later, we will see that this means that electrons in adjacent atoms have slightly different energies.)
The states with angular momentum nonzero have a higher energy than those with angular momentum zero (because of the extra repulsion term in the effective potential energy that comes from conservation of angular momentum). For any given principal quantum number, the lower-energy states will be filled first. The lowest states are s-states (angular momentum zero), followed by p-states (angular momentum 1), d-states (angular momentum 2), etc. So the 1s states fill, then the 2s, then the 2p, then 3s, then 3p. Interestingly, the 3d states have an energy higher than that of the 4s state, so it fills after the 4s, but before the 4p.
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